Optical filter layer

ABSTRACT

Optical filter layer containing in polyvinyl alcohol a filter dyestuff of the formula   WHEREIN R1 and R2 denote hydrogen atoms, halogen atoms or lower alkyl groups, R3 and R4 denote hydrocarbon radicals which may carry further substituents and X1 denotes an anion. The filter layers possess a very good fastness to light.

United States Patent Kitzing et a1.

[ 1 Dec. 18, 1973 OPTICAL FILTER LAYER Primary ExaminerNorman G. TorchinAssistant Examiner-J. P. B. Brammer Art0rney.1oseph G. Kolodny et a1.

[57] ABSTRACT Optical filter layer containing in polyvinyl alcohol afilter dyestuff of the formula wherein R and R denote hydrogen atoms,halogen atoms or lower alkyl groups, R and R denote hydrocarbon radicalswhich may carry further substituents and X, denotes an anion. The filterlayers possess a very good fastness to light.

7 Claims, 5 Drawing Figures rel. log E rel. log E rel. iog E OPTICALFILTER LAYER Colour originals can either be copied successively withblue, green or red copying light or, preferably, by a single exposurewith white light, onto colour copying materials. The copying material asa rule carries an upper layer sensitive to blue, a middle layersensitive to green and a lower layer sensitive to red. On exposure towhite light (so-called subtractive copying method) the layer sensitiveto blue should only respond in a part of the spectrum (for example 400500 nm), whilst the layer sensitive to green should only respond inanother part of the spectrum (for example 500 600 nm). To avoid anoverlap (cross-talk) of the sensitivities, it is customary to use anorange filter which is cast onto the material or'is pushed, as aseparate filter, into the path of the beam of the copying instrument andwhich filters out of the white light the wavelengths where sensitivitiesoverlap.

in this way, an improved blue-green separation is obtained. Such aprocess is described, for example, in French Patent Specification1,248,376.

The more the sensitivity of the layer sensitive to blue and of the layersensitive to green overlap, the more important it is to use an effectiveorange filter. The overlap is particularly troublesome if attempts aremade to increase the sensitivity of a silver bromide emulsion layerwhich is sensitive to blue by adding a blue sensitiser or by using asilver bromide emulsion containing iodine. in fact, these measures notonly lead to the desired increase in sensitivity but also to anundesired broadening of the sensitivity range towards longerwavelengths, for example as far as 520 nm.

The overlap of the sensitivities is also very particularly troublesomeif the layers are dyed in their sensitivity range, either with filterdyestuffs to increase the image sharpness or with image dyestuffs suchas are used in the silver dye bleach process. Thus, in a layer sensitiveto blue, dyeing with a yellow dyestuff depresses the sensitivity in theshort-wavelength blue region, whereby the sensitivity in thelong-wavelength blue region is relatively accentuated. Similarly, dyeinga layer sensitive to green with a magenta dyestuff depresses thesensitivity in the absorption range of this dyestuff, for example at 540to 560 nm, whereby the sensitivity in the boundary regions, for exampleat 490 to 510 and 570 to 600 nm, is relatively accentuated.

For the reasons which have been given, it has proved necessary, forcopying colour images with white light onto copying materials withoverlapping blue-green sensitivities, especially onto copying materialswith a layer sensitive to blue and dyed yellow and a layer sensitive togreen and dyed magenta, to insert into the path of the beam of thecopying light a copying filter which possesses a narrow absorption bandat about 500 nm but possesses a high transmission outside the absorptionband. The condition of having the narrow absorption band and the hightransmission results from the fact that at shorter and longerwavelengths the absorption of the yellow and magenta image dyestuffsalready influence the sensitivity of the emulsion so unfavourably thatan additional light absorption by the copying filter must be avoided inthese regions.

This condition is fulfilled by the dyestuffs of the formula In theformula (l), R, and R independently of one another, denote a hydrogenatom, an alkyl group with at most 4 carbon atoms or a halogen atom and Rand R independently of one another, each denote a hydrocarbon radicalwhich is optionally substituted further, and X, denotes an anion.

Though these filter dyestuffs are optically ideal, they possess only aninadequate fastness to light in the customary layer materials. lncontinuous operation. they therefore had to be replaced frequently.Surprisingly, it has now been found that the fastness of light of thesedyestuffs can be improved ten-fold to hundred-fold if they are embeddedin polyvinyl alcohol instead of in gelatine. Appropriately, a polyvinylalcohol is used whichis manufactured by extensive saponification of"polyvinyl acetate and contains at most 3 mol per cent of acetyl groups.The dyestuffs can be stirred into the aqueous solution of the polyvinylalcohol in the form of a solution, for example in methanol. This isappropriately done at 40C and in concentrations of 0.5 to 5 percent. Inaccordance with the desired optical density the amounts, relative to thedry polyvinyl alcohol, can

vary within certain limits, for example 0.1 to 1 percent. This yieldsmixtures which can be filtered perfectly and show no turbiditywhatsoever. For technical reasons concerned with casting it is adivsableto add a gelling agent for the polyvinyl alcohol when manufacturing thefilter layer from the dyestuff and the aqueous polyvinyl alcohol. As isknown, electrolytes, such as ammonium sulphate, aluminum sulphate,tannin and aluminium triformate have a more or less pronouncedcoagulating action on polyvinyl alcohol. The preferred gelling agent orcoagulating agent is sodium borate (borax).

Amongst the dyestuffs of the formula (1), those of the formula Bar Ruwherein R and R independently of one another, denote a hydrogen atom, amethyl group, an ethyl group, a chlorine atom or a bromine atom, R and Rindependently of one another, denote an alkyl group with at most 18carbon atoms, a lower hydroxyalkyl group or alkylcarboxylic acid group,and X denotes a chloride, bromide, iodide or perchlorate ion, areparticularly effective.

Further dyestuffs to be singled out are those of the formula wherein Rdenotes a methyl or ethyl group, X denotes a bromide, iodide orperchlorate ion and R and R have the indicated meaning, as well asdyestuffs of the formula H50: CH1

is particularly preferred.

Certain dyestuffs of the formula (I) are known and such dyestuffs can bemanufactured according to known methods (see US Patent Specification2,307,916).

Filters of the composition according to the invention can be usedwithout noticeable damage for numerous exposures, in some cases for atotal exposure time of 24 hours. The copies produced with the aid ofsuch a filter on transparent or opaque silver dye bleach copyingmaterials show a better separation of the colour shades than can beachieved with known filters of which the absorption band is broader,spectrally'smudged or of a different shape.

The filter according to the invention preferably has an optical densityof 0.5 to 2.0. It can be in the form of a self-supporting film or becast onto any desired transparent carrier such as glass, cellulosetriacetate or polyester. It may also be appropriate to locate it betweentwo transparent carrier layers. Thus, for example, a covering layer ofpolyvinyl alcohol, which can contain a UV-absorber, can be applied tothe filter layer. If appropriate, a carrier consisting of organicmaterial can also contain a UV-absorber, in which case the carrier isturned towards the light source during use.

EXAMPLE 1 2 litres of a 5% strength aqueous solution are prepared from alow-viscosity, so-called fully saponified saponin solution are added at40C, whilst stirring. Thereafter the mixture is filtered and theviscosity is adjusted to 9.2 cp by adding water. The pH value of theresulting ready-to-cast mixture is 8.2. A layer of 7.5 .1. (in the drystate) is produced on a photographic transparent layer carrier, forexample a carrier of cellulose acetate, at a casting temperature of 40Cand a casting speed of 9 m/minute. An identical casting mixture withoutaddition of the filter dyestuff is manufactured analogously. This secondcasting mixture is cast, as a protective layer of the same thickness, ontop of the filter layer. The optical density of the filter thusmanufactured is 0.95, measured from the transmitted light at theabsorption maximum. The absorption curve is represented in FIG. 4.

The fastness to light of the filter manufactured in this way is veryhigh, as is shown by the following comparison experiments: the filterwas inserted into a commercially available enlargement apparatus for theproduction of colour copies and for this purpose it was introduced intothe drawer provided for receiving colour filters. At an illuminationintensity of about 2,000 Lux in the filter plane, the filter was exposedto 4,000 exposures, with the individual exposure time being 14 secondsand a pause of 14 seconds being maintained after each exposure. Afterthese 4,000 exposures the filter with the dyestuff embedded in thepolyvinyl alcohol showed a decrease in density of 1 1 percent (FIG. 4).

A filter manufactured by way of comparison with the same dyestuff in theindicated concentration, but cast in gelatine and not in polyvinylalcohol, underwent a loss in density of 68 percent after 4,000 exposuresunder the identical conditions (FIG. 5). If instead of the dyestuff ofthe formula (5) the dyestuffs of the formula Ran listed in the tablewhich follows are used and in other respects the indicated procedure isfollowed, similar results are obtained.

TABLE )imax.

21 31 Rn X11 (methanol) H C2H5 CzHs l 502 H C1115 01H; I 498 II CzHg,C2115 Clot 498 H C2115 C2115 C104 501 II ll-CQIIH C1115 C10. 49!) ClCHz-CII:COOI[ Czlh I 502 C H3 CH2CI'I2C O O H C2115 I 508 II CH3(CH2):OII Dr 503 II C 115 C2115 1' 502 CH3 CzH5 C2115 I 502 If theprocedure described above is followed but instead of the abovementioneddyestuffs those which possess the same cation as described in formulae 110 but of which the anion X is a chloride, benzenesulphonate,p-toluene-sulphonate, ethylsulphate, methylsulphate, tetrafiuoborate,tetrafluotitanate, hexafluoantimonate, hexachlorostannate,hexachloroantimonate, tetrachloroaurate, tetrachloroaluminate ortetrachloroferrate anion, analogous results are obtained.

3,779,937 6 EXAMPLE 2 manner can be seen from H08. 1 and 2. It isclearly recognisable that the green and the red spectral region are wellseparated in both cases (FIG. 1 and 2). In the case of the exposurewithout the copying filter the sen- 5 sitivites between the blue and thegreen spectral range A copying material for the silver dye bleachprocess is prepared on a transparent carrier. in the layer sensitive tored the material contains the cyan image dyestuff of the formula HO;S\/SO;H trio-0 i-on. H0;s- -so;rr

in the layer sensitive to green it contains the magenta overlap greatlyThe undesired gh i i i y image dyestuff of the formula of the layersensitive to blue, containing the yellow .7 7 IS 11015 soar Ii ?-N=NNHOCNHC-HNC o-HN N=N 7 NH, 7 Hots 7 V v A sour Ha r and in the layersensitive to blue it contains the yellow image dyestuff, is caused bythe emulsion containing image dyestuff of the formula silver iodide andby the presence of a blue sensitiser.

H035 3C CH3 SOQH l -N:N-NH..OC C0 HN N=N m l, I l 4 -CH3 II3CO sour1103s The same silver bromide-iodide emulsion is used for Thesensitivity in this spectral region is additionally faalllight-sensitive gelatine layers. The individual layers voured by theyellow image dyestuff which no longer are sensitised with the followingdyestuffs: absorbs sufficiently in this region.

The unfavourable sensitivity distribution in the layer CZH5 sensitive togreen results from the co-operation of the J embedded magenta dyestuffwith the green sensitiser. Ha H! A particularly objectionable factor isthe sensitivity at g N I 6 40 500 to 510 nm being too high in comparisonto the sen- CH: sitivity at 550 nm.

[ On exposure using the copying filter according to Ex- Z ample 1 (FIG.2) it can be seen clearly that both the exooH cessively long-wavelengthpart of the layer sensitive to blue and the excessively short-wavelengthpart of the layer sensitive to green are corrected. This also eliminatesthe colour shifts caused by the excessive overlap Red sensitiser S OCzHs 19 in the blue and green spectrum region when producing \g/ colourcopies by the subtractive copying method.

50 We claim:

1. Optical filter layer the substrate of which consists Green sensitiser(sensitisation curve: Figure 3) substantially of polyvinyl alcohol whichlayer contains ClHa a filter dyestuff of the formula N S o 0 (3:5 \CH1 zI I =Hn C-CH=CH-CH=C H xu I 3,, 53/ \N 1 J l I CHI 0 I i Rn Bluesensitiser V g ,,4- A

I wherein R, and R independently of one another, de- Thls mammal exposeda wedge speFtrograph note a hydrogen atom, an alkyl group with at most 4(grey wedge) under the copying filter according to Excarbon atoms or ahalogen atom R3 and R4, indepem ample 1 and is then processed in theusual manner by the silver dye bleach process.

dently of one another, each denote a hydrocarbon radical which isoptionally substituted further and X,

The difference between the image thus obtained and denotes an i a plnfage which has been Produced with" 2. Optical filter layer accordingto claim 1, the filter out using the copying filter but otherwise inexactly the d t ff f hi h corresponds to the formula wherein R and Rindependently of one another, denote a hydrogen atom, a methyl group, anethyl group, a chlorine atom or a bromine atom, R and R independently ofone another, denote an alkyl group with at most 18 carbon atoms, a lowerhydroxyalkyl group or alkylcarboxylic acid group and X denotes achloride, bromide, iodide or perchlorate ion.

3. Optical filter layer according to claim 2, the filter dyestuff ofwhich corresponds to the formula I Rn S R 2- CH /CH2 N wherein R denotesa methyl or ethyl group, X denotes a bromide, iodide or perchlorate ionand R and R, have the meanings given in claim 2.

4. Optical filter layer according to claim 2, the filter dyestuff ofwhich corresponds to the formula wherein both R denote hydrogen atoms ormethyl groups or one R denotes a hydrogen atom and the 6. Optical filterlayer according to claim 1, the substrate of which consists of apolyvinyl alcohol retaining at most 3 percent of acetyl groups.

7.- Optical filter layer according to claim 6, the substrate of whichconsists of a polyvinyl alcohol which has been treated with a gellingagent.

UNITED STATES PATENT OF FlCE CERTIFICATE OF CORRECTION "MM" 13'-3QIY2,Q3Z- Dated December 18, 1973 Inventorg's) KAI NEE KITZING ET AL Itis certified that error appears in the above-identified patent andthat'saidLetters Patent are hereby corrected as shown below:

Change the formula in claiml to read as follows:

UNITED STATES PATENT OFFICE CERTIFICATE OF COREECTEN Patent .No.3,779,937 I V Dated DGCmbGI 18, 1973 -Inventor a RAINIER KITZING ET ALPage 2 It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

In column 7, claim. 3, change the left-hand portion'of the structuralformula to read as follows:

Signed and sealed this 24th day of December 1974.

(SEAL) Attest:

were M. crasor JR. c. IMF-{SHALL DANN Attesting Officer Commissioner ofPatents FORM PO-IOSO uo-tm USCOMM-DC 603756 69 0 u 5 GOVERNMENT wmnmcOFFICE: 1969 0-355-334

2. Optical filter layer according to claim 1, the filter dyestuff ofwhich corresponds to the formula
 3. Optical filter layer according toclaim 2, the filter dyestuff of which corresponds to the formula 4.Optical filter layer according to claim 2, the filter dyestuff of whichcorresponds to thE formula
 5. Optical filter layer according to claim 4,the filter dyestuff of which corresponds to the formula
 6. Opticalfilter layer according to claim 1, the substrate of which consists of apolyvinyl alcohol retaining at most 3 percent of acetyl groups. 7.Optical filter layer according to claim 6, the substrate of whichconsists of a polyvinyl alcohol which has been treated with a gellingagent.